Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

In 1997, the proportion of sperm injection treatments — in which sperm is injected into an egg — compared to in vitro fertilization was 44 percent across Europe. By 2001, sperm injection accounted for 48 percent.

The latest survey found there were more than 122,000 sperm injection treatments in Europe in 2002, compared with 113,000 in vitro fertilization, or IVF, treatments, pushing the proportion of injection up to 52 percent of the total.

Experts said Wednesday there are many possible explanations for the increasing popularity of the sperm injection approach.

The numbers could be showing that infertility may now affect more men than women.

However, they could also reflect the possibility that doctors in private clinics are increasingly opting for the more sophisticated sperm injection because it brings in more money than IVF, said Dr. Anders Nyboe Andersen, head of the fertility clinic at Copenhagen University, who conducted the survey on behalf of the European Society of Human Reproduction and Embryology.

It could also mean that men with infertility problems are now more willing to seek help, or that the technology is only now being widely adopted.

“The truth is we don’t know” the reason for the increase, said Andersen, presenting his findings at the organization’s annual conference.

Globally, about 30 percent of infertility cases have been linked to medical problems in men, 30 percent to problems in women, 20 percent to joint problems and the remaining 20 percent to unknown causes.

The first baby produced by in vitro fertilization, where an egg is placed in a dish with thousands of sperm, was born in 1978. The technique is effective in circumventing fallopian tube blockages in women as well as a wide range of male and female problems. However, if there are not enough sperm or if they are of poor quality, fertilization in the dish can be impossible.

To overcome that problem, the technique of intracytoplasmic sperm injection was developed. The first baby using the technique was born in 1992. That approach involves injecting a single sperm into the egg. It also bypasses the problem of egg shells being too tough for sperm to naturally break through.

Doctors may be opting now for sperm injection more often than IVF because they believe it has a better chance of producing suitable embryos, which can be important for patients who are paying for the treatment and want a better chance of a baby on the first attempt, Andersen said.

It may also have overtaken IVF because infertility is becoming proportionally less of a female problem, said Dr. Hans Evers, a professor of reproductive medicine at Academic University in the Netherlands who was not connected with the research.

That’s because condom use during the European AIDS crisis in the 1980s protected women from fallopian tube damage caused by other sexually transmitted infections, such as chlamydia, he said.

However, Andersen said he cannot rule out the possibility that the figures reflect a real worsening of male infertility.

“Perhaps the data on declining sperm quality are true, and maybe environmental factors are playing an increasing role as the planet becomes more polluted and factors that disrupt the (hormone) system enter the food chain,” Andersen said.